Humphries, john
Groiler International, 1993
Buku Teks
Hughes, G. David, author
Addison-Wesley, 1983
Buku Teks
Spiro, Rosann L., author
McGraw-Hill-Irwin, 2003
Buku Teks
Canfield, Bertrand R., author
Prentice-Hall, 1961
Buku Teks
Still, Richard R., author
Prentice-Hall, 1958
Buku Teks